The present invention generally relates to an image forming apparatus in which a plurality of developing devices are arranged.
Conventionally, an image forming apparatus is known in which a plurality of developing devices selectively operable for developing electrostatic latent image are arranged at a side of an electrostatic latent image support member. In the apparatus, since toner in the developing devices is consumed by development, replenishment of toner corresponding to consumption of toner must be suitably performed.
However, when documents having much solid portion are continuously copied, amount of consumed toner per one copying operation is extremely large. Therefore, although replenishment of toner is performed, density of toner in the developer in using is lower than a required level, resulting an image on a copied paper sheet in poor quality. Furthermore, when the apparatus has such function that copying operation is stopped to wait during density of toner reaches the required level, the waiting timer period is long and it is necessary for next copying operation to wait for a long time.